This invention relates to a propulsion device for a ship and particularly of the type which comprises an elongate rotatable body which is mounted on the ship in a generally upstanding direction for engaging air currents passing across the ship.
Ships have been known for many years in which such bodies in the form of cylinders, are used as the sole means of propulsion as a replacement for the fabric sails of the conventional type. Devices of this type are shown, for example, in U.S. Pat. Nos. 1,640,891 (Fritzel) and 1,674,169 (Flettner). The device is sometimes known as a Flettner rotor after the inventor of the basic principle.
As is well known, the rotating cylinder uses the Magnus effect to develop a force transverse to a passing air current. The direction of this force can be controlled by varying the speed of rotation of the rotor body.
For a full explanation of these effects, reference can be made to one or other of the above patents.
The Flettner device which was manufactured and used commercially was used as the sole means of propulsion of the ship or boat and steering of the ship was obtained by a rudder of conventional form. However, such an arrangement is not commercially acceptable in relation to modern requirements for manoeuverability and propulsion force even in zero air movement conditions.